Method of rust proofing treatment of metals



p 1967 SUSUMU NISHIGAKI ETAL. 3,342,710

METHOD OF RUST PROOFING TREATMENT OF METALS Filed July 25 1963 E I F3 JI.M g .m n a t a0 m o w 2 t6 1 3 g .1 i a F ml w e o T s -IIF'LIIFI' m w w w m nwumwho pmsn 32 o mamm I0 I00 I csm wmamono umsh wa s: o mudm r W K L 2 \l .l 4% m s m m m w t b 80 i M ll\ 90 8 m r O 0 a r 56 p 2 u 7 s f n s. q a 0 m t 0. m. 4 1 a m 0 t W e 0 1 F T s d h 2. m a 0 S gm mm mfiwmho p wa s: o ovmm Salt water spray time (hr) vmpmmno pm?" $0 23 o ovum vmpmmpo pm? 3 22 no 3mm Salt. water spray time (hr) 5 m R m m m m m MJM 4 wmhmo Z2 M 4 KV m N M o M 0 7 s m e w u M u T 7 United States Patent M 3,342,710 METHOD OF RUST PROOFING TREATMENT OF METALS Susumu Nishigalri, Mizuho-ku, Nagoya, Takao Nakamura,

Midori-ku, Nagoya, Takeshi Kusaka, Nishi-Kasugaigun, Aichi, and Takeshi Yano, Showa-ku, Nagoya, Japan, assignors to NGK Insulators, Ltd., Nogoya, Japan, a corporation of Japan Filed July 25, 1963, Ser. No. 297,513

Claims priority, application Japan, July 27, 1962,

37/31,284; Sept. 4, 1962, 37/37,383; Mar. 27,

1963, 38/15,531; June 5, 1963, 38/29,215; June 8 Claims. (Cl. 204-56) The present invention relates to the surface treatment for providing corrosion resistance to the surface of metals.

It is an important problem to give anti-corrosivity to the surface of metals and for this purpose various methods of plating of metals have long been tried in order to provide fine appearance and corrosion resistance to metal products and some of them have been practically used with some effect, however, they are expensive.

Recently, inexpensive casting products have been made by a die-casting process using zinc or light alloys and are utilized for various purposes but such products require anti-corrosive plating for preventing surface deterioration. Due to corrosion, copper alloys such as brass are liable to lose their fine appearance so that they often need expensive plating.

The principal object of the invention is to add corrosion resistance to corrosible metals by applying inexpensive and easy surface treatments to such metals.

The present invention relates to a method of an anticorrosion treatment of metals using an aqueous solution consisting of a mixture of a beryllium salt and one or more chromates or bichromates to treat the surface of the metals, more particularly, by dipping such metals in the treating solution and if necessary, by passing electric current through the solution and metals, thereby providing transparent and compact anti-corrosive coatings on the surface of metals.

Various methods for the surface treatments of metal parts of household utensils, all machines and instruments have heretofore been investigated and developed, yet there remain still many defects in the appearance and rust prevention and as to the transparence, compactness and heat resistance of the coating sufiicient results are not yet necessarily obtained and there still remains difiiculties in attaining easier and more economical treatment methods.

At present, the chromate process is broadly used for the rust proof treatment and applied to zinc, cadmium, copper, iron and the like metals and its rust proofing ability is excellent, yet there are still defects in spoiling appearance due to coloring of uneven golden and brown color and deficient in refractory nature. If in order to improve the appearance a dilute solution is used or alkali solution is used for decoloring it spoils rust proofing nature so that it could not provide excellent anti-corrosion treatment to provide transparent coating.

According to the method of the invention a transparent and compact anti-corrosive and refractory coating can be easily provided on the surface of a desired metal without spoiling appearance of the base metal by wetting with the solution, more particularly, dipping the metal to be treated into the solution and, if necessary, by applying electrolytic treatment in parallel thereto so that it has a novel characteristic as the rust prevention of metals.

Now the method of the invention will be explained further in detail:

(1) Dipping Process:

The specific results of the invention can be obtained by using a special treating solution which consists of a 3,342,710 iatented Sept. 19, 1957 beryllium salt added with one or more of chromates or bichromates to prepare a mixed aqueous solution having a suitable pH value by adjusting its acidity and after the surface of the metal to be treated is removed from oil and fat and cleaned by washing with acid the metal is dipped into the aqueous solution or the metal is wiped with the aqueous solution or wetted by spraying the solution, then the liquid on the surface is wiped off by rubber rolls and dried at a temperature from room temperature to 200 C.

As beryllium salts use is made of beryllium sulfate, beryllium nitrate, beryllium halide, basic beryllium acetate, beryllium citrate, beryllium tartrate, beryllium oxalate, sodium tetrafluoro beryllate and the like inorganic or organic beryllium salts, and as chromates, chromic acid, sodium chromate, and as bichromates, sodium bichromate, potassium bichromate may be used.

The concentration of beryllium in the. solution is preferably taken within the range of 0.05 to 5 g./lit. as Be component and the concentration of chromium is preferably taken within the range of 0.5 to 30 g./lit. At a concentration below this range the anti-corrosion property is inferior, while at a higher rate the coating is colored and a transparent coating can not be obtained and moreover, the improvement in the anti-corrosion effect is not found.

For a better understanding of the invention reference is made to the accompanying drawings, in which:

FIG. 1 shows curves illustrating the relation between salt water spraying time and the rate of rust creation in the application of the method of the invention;

FIGS. 2-(a) and -(b) are characteristic curves illustrating the relation between salt water spraying time and the rate of rust creation when wetting agent and reducing agent are added respectively;

FIG. 3 is a diagram showing the relation between pH of the treating solution and the rate of rust generation;

FIG. 4 illustrates curves showing the relation between the salt water spraying time and the rate of rust generation similar to FIG. 1 when the temperature of the treating solution is taken as parameter; and

FIG. 5 shows curves illustrating the comparative test results of conventional rust proof treating process.

Referring to FIG. 1, the curves A, B, C, D and E illustrate characteristic curves showing the relation between the salt water spraying period and the rate of white rust created as the results of exepriments treated by each aqueous solution prepared according to the following compositions:

(A) BeSO 4H O 1.5 g./lit.; CrO 7.5 g./lit. (B) BeSO 4H 0 3.0 g./lit.; CrO 3.0 g./lit. (C) BeSO 4H O 6.0 g./lit.; CrO, 6.0 g./lit.

.(D) BeSO 41-1 0 9.0 g./lit.; CrO 9.0 g./lit.

(E) BeSO 4H O 15.0 g./lit.; CrO 15.0 g./lit.

By adding to the treating solutions of the above described compositions less than 5% of Wetting agent or reducing agent further improved uniform coating can be obtained. As the wetting agent, triethanolamine, coconut amine or stearyl propylene diarnine and their ethylene oxide added derivatives, alkanol or phenol ether type derivatives are effective since such agents improve the quality of the coating by elfecting both catalytic and surface active agents on the surface of metals. As the reducing agents use is made of an organic reducing agent having an aldehyde group or that producing aldehyde during the reaction such as can sugar, glucose, vanillin, hexamethylenetetramine, or inorganic reducing agent such as sodium hypophosphate which gives no detrimental results even when it remains in the coating.

FIG. 2-(a) illustrates the effects of the addition agents, wherein The curve B illustrates the experimental results with the composition of BeSO -4H O; 6.0 g./lit. CrO 6.0 g./lit.,

F illustrates the result when 0.6% of hexamethylene tetramine is added to the composition of E,

G shows that when 0.6% of glucose is added to the composition E,

H shows that when 0.6% of sodium hypophosphate is added to the composition E,

I shows that when 0.6% of coconut amine derivatives is added similarly,

J is that when 0.6% of cane sugar is added similarly.

These curves are characteristic curves illustrating the relation between the time of spraying the above salt water and the rate of creating white rust.

FIG. 2-(b) illustrates the relation between the addition percent and the rust creating rate checked after the lapse of time of 120 hrs. of the salt water spray test specified by I IS rule When triethanolamine and cane sugar are added respectively to the standard treating solution having the composition of BeSO -4H O 6.0 g./lit., CrO 6.0 g./lit. expressed by K and L respectively.

Instead of adding reducing agents trivalent chromium may be previously added to the treating solution to provide the coating having improved rust proof nature similarly. As the trivalent chromium salts, chromium alum, chromium hydroxide, chromium sulphate and chromium nitrate, etc. may be used. The concentration of the trivalent chromium is taken preferably within the range of 0.1 to 10 g./lit of Cr element. Below the above range anti-corrosion property becomes poor and at a higher rate the product is colored and no transparent coating is obtained and also the anti-corrosion effect is not improved.

Nex, the effect of pH value of the above mixed aqueous solution will be described.

For obtaining compact coating film a good result is obtained by adjusting the value of pH to 3 to 6. The relation between pH and the anti-corrosive nature is as shown in FIG. 3 and within the range of 3 to 6 pH the transparent and compact film coating can be obtained, while above pH 6 a large amount of beryllium hydroxide deposits so that the treatment becomes more difficult and below pH 3 the anti-corrosive effect becomes worse. FIG. 3 illustrates the results of salt water spray tests according to 118 after the lapse of 72 hrs. when the composition of the treating solution is BeSO -4H O 6.0 g./lit., CrO 6.0 g./ lit. with different values of pH.

The treating solution may be used at room temperature, but when it is heated to a temperature of 40 to 70 C. it provides a coating having superior anti-corrosive property. FIG. 4 shows the effect of the temperature of the treating solution by M when the temperature is room temperature and by N when the temperature is 40 C. and by P at 60 C. respectively and each rust creating rate when using the treating solution of BeSO -4H O 3.0 g./lit., CrO 3.0 g./lit.

The term dipping in the specification is to be understood to include the immersion into the solution, wiping, coating or spraying and the duration of dipping i preferably 2 to 60 seconds and the longer treatment time than this can not expect the further improved results.

Accordingly to the dipping method of the invention there is formed a coating having excellent rust proof and heat resistance on the surface of the metal to be treated containing essentially to 30% of BeO, mainly consisting of 2BeO-CrO or Cr O -2BeO-CrO and it is assumed that the coating is formed by the following reaction mechanisms By usinga treating solution having a strong acidity the coating containing a large amount of BeO can be obtained mainly according to the formula (1), and by the formula (2) when using a substantially neutral treating solution.

The wetting agent such as amines having the side chain of polyvalent alcohol or polyoxyethylene forms a stable chelate compound and at the same time the hydrophilic radical adheres to the surface of the treated metal to form an adherent uniform coating. Meanwhile hexavalent chromium is partly reduced to trivalent chrominum during the drying stage to provide a film having further superior anti-corrosive property.

According to the method of the invention a transparent and compact coating having 0.01 to 0.2;; thickness is produced without spoiling the appearance of the base metal and the rust proofing property of the film is exceedingly good and prevents rusting and decoloration of the base metal by corrosive gases and liquids, such as water vapour, sodium sulfide, hydrogen sulfide, ammonium and hydrogen chloride gases, caustic soda and the like. The comparative results according to the salt water spray test specified by 118 Z 2371 with the conventional transparent colorless chromic acid treatment and chromate treatment are shown in FIG. 5.

Referring to FIG. 5, Q illustrates the result according to the treatments of chromic acid (1%), R is that of chromate treatment and S the treatment according to the invention.

Further according to the treatment of the invention such as dipping method the heat resisting (refractory) film up to 250 to 400 C. can be obtained and moreover it can be soldered, and the insulation resistance is considerably low so that it can be applied to various electrical purposes. These characteristics have not been attained by heretofore known anti-corrosion treatments such as chromic acid treatments.

Moreover the treating solution of the invention is very dilute and the method of treatment can be simply carried out by dipping, wiping or spraying as above explained so that it has advantage from an economical point of view.

The rust proof treatment of the invention can be broadly applied to various purposes and it is effective in preventing rust, decoloration and improving the heat resistance for the metals such as zinc alloys, copper, copper alloys, aluminum, aluminum alloys, magnesium, magnesium alloys, cadmium, cadmium alloys, white metal, mild steel, stainless steel and the like iron and steel products, gold, silver, nickel and nickel alloys, chromium and the like metals and the plated products thereof and can be broadly and etfectively applied to general household utensils, electrical parts, machines and machine parts, gold and silver decorations, zinc plated iron plates and the like building construction materials, fixtures and the like.

(2) Combined method of dipping and electrolysis:

The method of the invention can be carried out by using an aqueous solution mainly containing beryllium salts added with chromic acid, sodium bichromate, potassium bichrornate and the like chromium salts and by dipping the metal to be treated therein and by passing electric current therethrough under a definite condition with the treated metal as a cathode, thereby producing oxidized film containing anti-corrosive beryllium and chromium, which is transparent, compact and exhibits an anti-corrosive property.

It is considered that the oxidized film coating is produced by electrolyzing an aqueous solution containing beryllium salts to discharge Be++ on the surface of the metal constituting a cathode and at a same time oxidized by the chromic acid, thereby forming the oxidized beryillium coating directly on the metal surface and its reaction is shown by the following formulas as for instance:

That is, it is considered that the transparent, compact and anti-corrosive coating having complex compositions such as BeO, Cr O CrO BeCrO BeCr O is formed on the surface of the metal.

The method of surface treatment of the invention will be further explained in detail as follows:

(1) Preparation of the solution:

As the source of beryllium, beryllium sulfate, beryllium nitrate, beryllium halide, basic beryllium acetate, sodium tetrafluoro beryllate and the like beryllium salts are used. As the source of chromate, chromic acid, sodium chromate and as bichromate, sodium bichromate, potassium bichromate is added thereto to provide a mixed solution and the pH value of this solution is adjusted to 2 to 7 by using an alkali such as ammonia water or caustic soda or an acid such as sulfuric acid. The metal to be treated is dipped into the aqueous solution to establish a cathode and using a lead plate, graphite plate or stainless plate and the like anti-corrosive conductive material or beryllium metal piece itself as an anode, the direct current is passed through these electrodes, then the metal thus treated is water washed and dried. If, furthermore, one or more of inorganic or organic salts of metals such as nickel, cobalt, titanium, zirconium, zinc, lead, chromium, tin, gold, silver, copper, rhodium, antimony, cadmium, aluminum, magnesium and the like is added to the above solution and electric current is passed in the similar manner as before more compact, and lustrous coating may be obtained and the anti-corrosive property can be further improved.

More particularly, an electrolyte which does not spoil the characteristics of coating, such as, sodium sulfate, and boric acid may be added, then the conductivity of the treating solution is improved and the film can be well coated. Further, by adding to 20% of the lustre and anti-corrosion improving agents of inorganic or organic material, such as compounds of arsenic, selenium, tellurium and sulfur, gelatin, saccharin, quinoline and the like further effect can be produced and also by adding less than of wetting agent or reducing agent it enables to obtain more homogeneous coating of better quality.

The wetting agents are preferably coconut amine, stearyl propylene diamine and their derivatives and the like amine system and also alkanol or phenol ether type derivatives.

Further, instead of adding the reducing agent to the treating solution the solution is preliminary added with trivalent chromium for the purpose of electrolytic treatment, then the coating having better anti-corrosive nature can be obtained. As the trivalent chromium, chromium alum, chromium hydroxide, chromium sulfate, chromium nitrate can be used and the concentration of the trivalent chromium is preferably 0.1 to 10 g./lit. of Cr component.

Arsenic, selenium, tellurium and sulfur compounds make the surface coating compact and hard and provide lustre and improve anti-corrosive nature, but more than 20% has no more improvement than that of less than 20% so that 20% is taken as a limit. Gelatin, saccharin and quinoline make the surface specially smooth and increase the corrosion resistance, but more than 20% has no effect of improving further so that it was taken as a limit. After the completion of the electrolysis the prodllcts should be well washed with water and dried. The coating thus obtained increases the lustre above that of the case when beryllium salts only are used in the solution and also the corrosion resistance is superior.

The treating solution of the invention is deteriorated during use by the metal to be treated. Since the treating solution is deteriorated as it is used it should be always maintained within the following range of composition in order to obtain a good coating.

(2) Current density:

The current density of the cathode for obtaining the best coating is 0.05 ma./cm. to 10 ma./cm. and with the current density less than that a homogeneous coating can not be obtained and with the larger current density the treated surface becomes coarse so that the compact coating is diflicult to obtain.

(3) Concentration of beryllium:

The concentration of beryllium in the electrolytic treating solution is preferably 0.05 g./l. to 1.0 g./l. and with a lower concentration than this range the transparent and compact coating can not be produced so that it is not suitable and with a higher concentration the treated surface becomes rough and loses lustre.

(4) The pH of the solution:

The pH of the solution is best at 2 to 7 and if the pH is larger than 7 beryllium hydroxide precipitates in the treating solution so that the concentration of beryllium ion necessary in the solution can not be obtained and moreover colloidal beryllium hydroxide precipitates on the surface of the cathode. If the pH of the solution is less than 2 the metal to be treated is attacked before electric current is passed and the treating solution is deteriorated so that a good coating can not be obtained.

( 5 Time necessary for electrolysis:

The time necessary for electrolysis depends upon the use of the articles to be treated, yet in order to improve the lustre, resistance to decoloration and corrosion the duration of 1 second to 20 minutes is preferable and more particularly in order to improve the corrosion resistance 2 to 20 minutes are preferable, yet if the electrolysis is continued longer than the above the beryllium discharged on the surface of cathode will become beryllium hydroxide to precipitate as the corroidal tate on the surface of the transparent and compact oxidized film initiary formed on' the surface, thereby disturbing the effective utilization of beryllium so that it is unsuitable.

(6) Condition of film:

The film thus produced on the metal improves its lustre compared with that before the treatment, yet as it is transparent and compact, the color of the base material to be treated is not changed. With low current density for a short period the thickness of the film is thin and was determined to be to 2,000 A. 'by measurement with the interference microscope and the existance of beryllium in the film was recognized by the spectroscopic analysis.

The coated film showed good corrosion resistance and maintained good condition in water vapour, sodium sulfide, hydrogen sulfide, ammonia, hydrogen chloride and the like corrosive gases and moreover, it has a large advantage in that a very dilute solution of beryllium is used for the treatment at a low current density for a very short time so that the cost of treatment is very low.

The present anti-corrosion surface treatment is particularly effective for all articles made by zinc die-casting or galvanized iron plates and also zinc plated articles, moreover, it shows effective results which can never be attained by the other plating solution for the improvement of discoloration and corrosion resistance for all metals such as light alloy products, copper and copper alloy products, white metal, iron and steel products, copper, chromium, nickel, rhodium, gold, silver, cadmium, antimony, tin, lead and the like various plated products. Moreover, the beryllium may be used as a very dilute solution and chromium is sufiicient with a much less quantity than that for the chromate treating solution so that the cost is very inexpensive. And also due to the fact that the coating is very thin substantially no increase of contact resistance is recognized so that it can be sufliciently used for electric materials such as electric contacts and the coated surface can be easily soldered. The metals to be treated may be of any metal so far as it has at least electric conductivity and it can be provided with practicable anti-corrosion coating by merely applying thereto the surface cleaning treatment so that the invention can be broadly utilized for household utensils in general, electrical parts, materials for building construction, ornaments and various machine parts etc.

. 7 Now the invention will be explained further in detail by means of examples.

Example 1 Beryllium sulfate g./lit. 6.0 Chromic acid g./lit. 6.0 pH (controlled by ammonia water) .8 Temperature of the solution, C 60 Into the above mentioned treating solution were dipped a zinc plate and a cadmium plate for 5 seconds respectively, then the solution attached to the plates was squeezed by means of rubber rolls and dried at 120 C. for 5 minutes, a transparent surface coating having thickness of 0.05 was obtained. According to the salt water spray test under the specification of HS Z 2371 each of the test pieces when untreated formed rust in 5 hrs., but using that subjected to the treatment of the invention no rust was recognized after the lapse of 60 hrs.

Example 2 Beryllium sulfate g./lit. 6.0 Sodium bichromate g./lit. 4.0 Alkanol amine, percent 0.5 pH (regulated by means of caustic soda solution) 5.0 Temperature of the solution, C 50 Into the above mentioned treating solution a silver plated plate, copper plate and brass plate were dipped respectively for seconds, then the solution attached to the plate was squeezed by rubber rolls and dried at 100 C. for 5 minutes and yielded the transparent film coating having thickness of 0.04 The article subjected to the above treatment showed entirely no discoloration after left for 10 minutes in hydrogen sulfide gas.

Example 3 Beryllium sulfate g./lit. 9.0 Chromic acid g./lit. 9.0 Cane sugar, percent 0.6 pH (regulated with ammonia) 5.5 Temperature of the solution, C 60 Into the above mentioned treating solution was dipped an iron plate for 5 seconds, then the solution attached to the plates was squeezed by means of rubber rolls and dried at 120 C. for 5 minutes and yielded a transparent film of 0.06 thickness. The iron plates subjected to the treatment of the invention showed substantially no rust after left for about 1 month in outdoors.

Example 4 Beryllium nitrate g./lit. 4.0 Chromic acid g./lit. 6.0 Chromium alum g./lit. 4.0 pH 3.5 Temperature of the solution, C 60 Into the above mentioned treating solution was dipped a zinc plate for 5 seconds, then the liquid on the plate was shaken off and dried at 120 C. for 2 minutes, then water washed and left at room temperature. The zinc plate thus treated was applied to the salt water test of JIS Z 2371 and ascertained that entirely no white rust was created after the lapse of 120 hrs. Further the reduction of weight by dipping the sample into water for 3 months was measured and it showed that the reduction was only A; of the chromate treated zinc plate and the surface appearance has entirely no change from that before the test.

Example 5 Beryllium sulfate g./lit. 3.0 Sodium bichromate g./lit. 3.0 Chromium sulfate g./lit. 1.0 pH 3.0 Temperature of the solution, room temperature, C.

Into the above specified treating solution was dipped a copper plate and electrolyzed with a lead plate as an anode and the copper plate as a cathode by passing electric current of 0.1 A./dm. then the plate was water washed and dried at C. for 5 minutes and yielded colorless transparent coating.

The sample thu treated showed no discoloration by placing in hydrogen sulfide gas for 2 hrs. or exposing it in ammonia gas for 5 hours and dipping in (5%) sodium sulfide solution for 10 minutes or, by subjecting it to the heat treatment at 300 C. for 30 minutes.

Example 6 Beryllium sulfate g./lit l5 Chromic acid g./lit 10 Chromium hydroxide g./lit 3 pH 3.5

A mild steel plate was subjected to electrolysis as a cathode in the above described solution with a lead plate as an anode by passing electric current of 0.05 A./dm. for 1 minute, then the mild steel plate was water washed and dried at 100 C. for 5 minutes, and then it was subjected to the salt Water spray test under the specification of 118 Z 2371 which showed that no rust wa created after the lapse of 15 hrs. The result of adhesion test of the paint by using melamine paint showed the superior adhesion to that of untreated steel plate.

Example 7 3.0 g. of beryllium sulfate tetrahydrate crystal, 1.0 g. of chormic acid and 3.0 g. of nickel sulfate heptahydrate crystal were dissolved in 1 lit. of water and it pH was adjusted to 5.5 with ammonia water. Into this solution was dipped a copper plate of 2.5 cm. x 4 cm. x 0.1 cm. after being defatted and washed with acid and water and electrolyzed as a cathode using lead plates as an anode with the current density of 0.2 ma./cm. for 7 minutes and after completion the plate was dried. In this case the lustre was better than that of beryllium sulfate solution and the lustre coefficient of beryllium only was 54.3%, while that of Example 7 was 63.7. This plate was similarly tested with sodium sulfide solution showing no change.

By using the above solution a brass plate of the same dimension wa subjected to the electrolytic treatment under the same condition and Was suspended in an enclosed container filled with concentrated ammonia water for 1 day, then the untreated plate was changed to dark green color but the treated plate showed no change.

Next a zinc plate of the same dimension was treated in the similar manner and left in water vapour at 120 C. for 2 days, then white rust formed on the untreated zinc plate but the treated one did not lose lustre.

Example 8 3.0 g. beryllium sulfate tetrahydrate crystal and 2.0 g. of chromic acid were dissolved in 1 lit. of water and its pH was adjusted to 5.8 by means of ammonia water. Into this solution were dipped a sufficiently defatted, acid and water washed copper plate, brass plate and iron plate as cathodes and electrolyzed by using a lead plate as an anode with current density of 0.5 ma./cm. for 5 minutes. After the completion of the electrolysis the plates were thoroughly water washed and dried at C. for 10 minutes to yield coatings on the metal surfaces. Each sample thus treated was suspended into conc. ammonia water in an enclosed container and left for 1 day, then the untreated samples were changed to dark green or gray color, whilst the treated samples showed no discoloration. Next, a zinc plate was treated in the similar manner and left in water vapor at 50 to 100 C. for 3 days, then white rust formed on the entire surface of the untreated sample but the treated sample showed no change.

The similarly treated copper plate was heat treated in the atmosphere at 230 C. for 2 hours, then the untreated sample changed to dark brown color but the treated sample showed no change.

Example 9 3.0 g. of beryllium sulfate tetrahydrate crystal, 3.0 g. of sodium bichromate and 2.0 g. of nickel sulfate heptahydrate crystal were dissolved in I lit. of water and its pH was adjusted to 5.5 with ammonia water. Into this solution were dipped a thoroughly defatted, acid and water washed copper plate and a lead plate to be used as an anode and electrolytic plating was effected with current density of 0.3 ma./cm. for 7 minutes and after completion the samples were dried in the similar manner as in Example 8. The samples were dipped into sodium sulfide aqueous solution for 1 minute, then the untreated sample was changed to dark brown color, but the treated sample showed no change.

What we claim is:

1. A method of forming a corrosion resistant coating on metal surfaces selected from the group consisting of Zinc, cadmium, silver, copper, iron metal and their base metal alloys which comprises applying on the metal surface an aqueous solution consisting essentially of a beryllium salt selected from the group consisting of beryllium sulphate, beryllium nitrate, beryllium halide, basic beryllium acetate, beryllium citrate, beryllium tartrate, beryllim oxalate and sodium tetrafluoro beryllate having a beryllium ion concentration in the range of from 0.05 to 5 g./lit., at least one compound selected from the group consisting of chromic acid, chromate and bichromates having a chromium ion concentration in the range of from 0.5 to 30 g./lit., and a wetting agent selected from the group consisting of coconut amine, triethanol amine, stearyl propylene diamine and phenol ether type derivatives present in an amount of less than 5% by weight based on the total amount of the aqueous solution, the pH of said solution being between 3 and 6.

2. A method of forming a corrosion resistant coating on metal surfaces selected from the group consisting of zinc, cadmium, silver, copper, iron metal and their base metal alloys which comprises applying on the metal surface an aqueous solution consisting essentially of a beryllium salt selected from the group consisting of beryllium sulphate, beryllium nitrate, beryllium halide, basic beryllium acetate, beryllium citrate, beryllium tartrate, beryllium oxalate and sodium tetrafluoro beryllate having a beryllium ion concentration in the range of from 0.5 to 5 g./lit., at least one compound selected from the group consisting of chromic acid, chromates and bichromates having a chromium ion concentration in the range of from 0.5 to 30 g./lit., and a reducing agent selected from the group consisting of cane sugar, glucose, vanillin, hexamethylene tetramine and sodium hypophosphate present in an amount of less than 5% by weight based on the total amount of the aqueous solution, the pH of said solution being between 3 and 6.

3. A method of forming a corrosion resistant coating on metal surfaces selected from the group consisting of zinc, cadmium, silver, copper, iron metal and their base metal alloys which comprises applying on the metal surface an aqueous solution consisting essentially of a beryllium salt selected from the group consisting of beryllium sulphate, beryllium nitrate, beryllium halide, basic beryllium acetate, beryllium citrate, beryllium tartrate, beryllium oxalate and sodium tetrafiuoro beryllate having a beryllium ion concentration in the range of from 0.05 to 5 g./lit., at least one compound selected from the group consisting of chromic acid, chromates and bichromates having a chromium ion concentration in the range of from 0.5 to 30 g./lit., and at least one trivalent chromium compound selected from the group consisting of chromium salts and trivalent chromium hydroxide having a trivalent chromium ion concentration in the range of from 0.1 g./lit. to g./lit., the pH of said solution being between 3 and 6.

4. A method of forming a corrosion resistant coating on metal surfaces selected from the group consisting of aluminum, magnesium, zinc, cadmium, silver, copper, iron metal and their base metal alloys which comprises dipping said metal into an aqueous solution consisting essentially of a beryllium salt selected from the group consisting of beryllium sulphate, beryllium nitrate, beryllium halide, basic beryllium sulphate, beryllium citrate, beryllium tartrate, beryllium oxalate and sodium tetrafiuoro beryllate having a beryllium ion concentration in the range of from 0.05 to 1.0 g./lit., at least one compound selected from the group consisting of chromic acid, chromates and bichromates having a chromium ion concentration in the range of from 0.5 to 30 g./lit., and a wetting agent selected from the group consisting of coconut amine, .triethanol amine, stearyl propylene diamine and phenol ether type derivatives present in an amount of less than 5% by weight based on the total amount of the aqueous solution, the pH of said solution being between 2 and 7, and said metal being a cathode, and passing an electric current having a density of 0.05 to 10 ma./cm. at a temperature in the range of room temperature to C. for from one second to 20 minutes through said solution.

5. A method of forming a corrosion resistant coating on metal surfaces selected from the group consisting of aluminum, magnesium, zinc, cadmium, silver, copper, iron metal and their base metal alloys which comprises dipping said metal into an aqueous solution consisting essentially of a beryllium salt selected from the group consisting of beryllium sulphate, beryllium nitrate, beryllium halide, basic beryllium sulphate, beryllium citrate, beryllium tartrate, beryllium oxalate and sodium tetrailuoro beryllate having a beryllium ion concentration in the range of from 0.05 to 1.0 g./lit., at least one compound selected from the group consisting of chromic acid, chromates and bichromates having a chromium ion concentration in the range of from 0.5 to 30 g./lit., and a reducing agent selected from the group consisting of cane sugar, glucose, vanillin, hexamethylene tetrarnine and sodium hypophosphate present in amount of less than 5% by weight based on the total amount of the aqueous solution, the pH of said solution being between 2 and 7, and said metal being a cathode, and passing an electric current having a density of 0.05 to 10 ma./cm. at a temperature in the range of room temperature to 70 C. for from one second to 20 minutes through said solution.

'6. A method of forming a corrosion resistant coating on metal surfaces selected from the group consisting of aluminum, magnesium, zinc, cadmium, silver, copper, iron metal and their base metal alloys which comprises dipping said metal into an aqueous solution consisting essentially of a beryllium salt selected from the group consisting of beryllium sulphate, beryllium nitrate, beryllium halide, basic beryllium acetate, beryllium citrate, beryllium tartrate, beryllium oxalate and sodium tetra- :fluoro beryllate having a beryllium ion concentration in the range of from 0.05 to 1.0 g./lit., at least one compound selected from the group consisting of chromic acid, chromates and bichromates having a chromium ion concentration in the range of from 0.05 to 30 g./lit., and at least one trivalent chromium compound selected from the group consisting of chromium salts and trivalent chromium hydroxide having a trivalent chromium ion concentration'in the range of from 0.1 g./lit. to 10 g./lit., the pH of said solution being between 2 and 7, and said metal being a cathode, and passing an electric current through said solution at a temperature in the range of room temperature to 70 C. for from one second to 20 minutes, thereby electrolyzing said solution.

7. An aqueous solution for forming a corrosion resistant coating on metal surfaces by electrolyzing the aqueous solution, which consists essentially of water, a beryllium salt selected from the group consisting of beryllium sulphate, beryllium nitrate, beryllium halide, basic beryllium acetate, beryllium citrate, beryllium tartrate, berylllll lium oxalate and sodium tetrafluoro beryllate having a beryllium ion concentration in the range of from 0. to 5 g./lit., at least one compound selected from the group consisting of chromic acid, chromates and bichrom-ates having a chromium ion concentration in the range of from 0.5 to 30 g./lit., and a wetting agent selected from the group consisting of coconut amine, triethanol amine, stearyl propylene diamine and phenol ether type derivatives present in an amount of less than 5% by Weight based on the total amount of the aqueous solution, the pH of said solution being between 2 and 7.

8. An aqueous solution for forming a corrosion resistant coating on metal surfaces by electrolyzing the aqueous solution, which consists essentially of water, beryllium salt selected from the group consisting of beryllium sulphate, beryllium nitrate, beryllium halide, basic beryllium acetate, beryllium citrate, beryllium tartrate, beryllium oxalate and sodium tetrafiuoro beryllate having a beryllium ion concentration in the range of from 0.05 to 5 g./lit., and at least one compound selected from the group consisting of chromic acid, chromates and bichromates having a chromium ion concentration in the range of from 0.5 to g./lit., and a reducing agent selected from the group consisting of cane sugar, glucose, vanillin, hexamethylene tetramine and sodium hypophosphate present in an amount of less than 5% by weight based on the total amount of the aqueous solution, the pH of said solution being between 2 and 7.

References Cited UNITED STATES PATENTS 2,733,199 1/1956 Wick 204-56 2,746,915 5/1956 Giesker et al 20456 2,868,679 1/1959 Pimbley 148--6.2 2,998,361 8/1961 Kitamura 204-58 X 3,084,111 4/1963 Strauss et al. 20451 JOHN H. MACK, Primary Examiner.

G. KAPLA'N, Assistant Examiner. 

1. A METHOD OF FORMING A CORROSION RESISTANT COATING ON METAL SURFACES SELECTED FROM THE GROUP CONSISTING OF ZINC, CADMIUM, SILVER, COPPER, IRON METAL AND THEIR BASE METAL ALLOYS WHICH COMPRISES APPLYING ON THE METAL SURFACE AN AQUEOUS SOLUTION CONSISTING ESSENTIALLY OF A BERYLLIUM SALT SELECTED FROM THE GROUP CONSISTING OF BERYLLIUM SULPHATE, BERYLLIUM NITRATE, BERYLLIUM HALIDE, BASIC BERYLLIUM ACETATE, BERYLLIUM CITRATE, BERYLLIUM TARTRATE, BERYLLIUM OXALATE AND SODIUM TETRALFUORO BERYLLATE HAVING A BERYLLIUM ION CONCENTRATION IN THE RANGE OF FROM 0.05 TO 5 G./LIT., AT LEAST ONE COMPOUND SELECTED FROM THE GROUP CONSISTING OF CHROMIC ACID, CHROMATES AND BICHROMATES HAVING A CHROMIUM ION CONCENTRATION IN THE RANGE OF FROM 0.5 TO 30 G./LIT., AND A WETTING AGENT SELECTED FROM THE GROUP CONSISTING OF COCONUT AMINE, TRIETHANOL AMINE, STEARYL PROPYLENE DIAMINE AND PHENOL ETHER TYPE DERIVATIVES PRESENT IN AN AMOUNT OF LESS THAN 5% BY WEIGHT BASED ON THE TOTAL AMOUNT OF THE AQUEOUS SOLUTION, THE PH OF SAID SOLUTION BEING BETWEEN 3 AND
 6. 4. A METHOD OF FORMING A CORROSION RESISTANT COATING OF METAL SURACES SELECTED FROM THE GROUP CONSISTING OF ALUMINUM, MAGNESIUM, ZINC, CADMIUM, SILVER, COPPER, IRON METAL AND THEIR BASE ETAL ALLOYS WHICH COMPRISES DIPPING SAID METAL INTO AN AQUEOUS SOLUTION CONSISTING ESSENTIALLY OF A BERYLLIUM SALT SELECTED FROM THE GROUP CONSISTING OF BERYLLIUM SULPHATE, BERYLLIUM NITRATE, BERYLLIUM HALIDE, BASIC BERYLLIUM SULPHATE, BERYLLIUM CITRATE, BERYLLIUM TARTRATE, BERYLLIUM OXALATE AND SODIUM TETRAFLUORO BERYLLATE HAVING A BERYLLIUM ION CONCENTRATION IN THE RANGE OF FROM 0.05 TO 1.0 G./LIT., AT LEAST ONE COMPOUND SELECTED FROM THE GROUP CONSISTING OF CHROMIC ACID, CHROMATES AND BICHROMATES HAVING A CHROMIUM ION CONCENTRATION IN THE RANGE OF FROM 0.5 TO 30 G./LIT., AND A WETTING AGENT SELECTED FROM THE GROUP CONSISTING OF COCONUT AMINE, TRIETHANOL AMINE, STEARYL PROPYLENE DIAMINE AND PHENOL ETHER TYPE DERIVATIVES PRESENT IN AN MOUNT OF LESS THAN 5% BY WEIGHT BASED ON THE TOTAL AMOUNT OF THE AQUEOUS SOLUTION, THE PH OF SAID SOLUTION BEING BETWEEN 2 AND 7, AND SAID METAL BEING A CATHODE, AND PASSING AN ELECTRIC CURRENT HAVING A DENSITY OF 0.05 TO 10 MA./CM.2 AT A TEMPERATURE IN THE RANGE OF ROOM TEMPERATURE TO 70*C. FOR FROM ONE SECOND TO 20 MINUTES THROUGH SAID SOLUTION. 